Hi D. - Unless you are malnourished and if you really have ADD, it is really unlikely that a special diet will help. I'm all for eating healthfully (fruits, veggies, whole grains, lean protein, good fats, etc)but the research on the diets does not support their effectiveness for most kids with ADD (and I say kids because I'm not sure that this HAS been researched with adults). I'm not going to say there aren't some cases out there where this has really helped - but it's probably a good idea to be really cautious. There's not enough research to say what a restricted diet woudl do to your body in the long term and some of the diets really lack important nutrients you need to function. It's also probably a good idea to get a medical check up and a good evaluation with a psychologist or psychiatrist to be sure your symptoms are due to ADD and not something else (like lack of sleep for example, or a thyroid condition, or even anxiety). Often insurance companies will cover part if not all of the evaluation and treatment of ADD.
Here are some websites on diagnosis and treatment of ADD in adults and one on ADD classes. You'll notice that it refers to ADHD - Basically there are three types of ADHD - ADHD Predominantly Inattentive Type (which people call ADD), ADHD Predominantly Hyperactive-Impulsive Type (mostly seen in young children), and ADHD Combined Type for people who have both sets of symptoms. If you're more the ADD type as an adult, you don't tend to be as impulsive (doing things or saying things before thinking them through) or as restless.
http://www.webmd.com/add-adhd/guide/adhd-adults?page=2
http://www.help4adhd.org/treatment/guides/WWK9
http://www.addclasses.com/
The most recommended treatments for adult ADD are behavioral and organizational skills coaching and medication. There have been many more studies in the past ten years about medication for adult ADD, and many of the ones used with children are also used with adults with good efficacy. But getting that evaluation I was mentioning is important - if you are also experiencing any symptoms of anxiety or depression, the medication choices may be different for you than if you don't experience those symptoms.
If you need referrals for an evaluation or coaching or any other treatment, feel free to send me a message!